Device for detecting compressor discharge gas temperature



Oct. 11, 1966 5, PARKER 3,278,111

DEVICE FOR DETECTING COMPRESSOR DISCHARGE GAS TEMPERATURE 0 1875 07 par/ 19F United States Patent 3,278,111 DEVICE FOR DETECTING COMPRESSOR DISCHARGE GAS TEMPERATURE Sidney A. Parker, Fort Worth, Tex., assignor to Lenuox Industries Inc., a corporation of Iowa Filed July 27, 1964, Ser. No. 385,433 Claims. (Cl. 23017) This invention relates to control apparatus for a hermetic refrigerant compressor and, more particularly, to a compressor protective device which is internal of the compressor and which is responsive to disharge gas temperature to terminate operation of the compressor motor upon attainment of a predetermined discharge gas temperature.

It is of primary importance in the design of modern day hermetic refrigerant compressors, that the compressor be protected under all conditions of voltage, ambience and load without unnecessary shutdown due to false sensing of temperature or pressure conditions. It has been known to provide the motor of a hermetic compressor unit with inherent motor protection. Basically, the inherent protector device responds to both winding temperature and motor current. Generally, the device is located on the winding or internally of the motor winding The device functions to sense the temperature that deteriorates insulation and responds to open the circuit to the compressor motor before any damage can be done. It thus protects the motor against the causes of motor over-heating and burn-out such as locked-rotor, stalling extreme overloads and gradual temperature rise within the motor.

An important factor influencing the lift of a hermetic compressor and the oil and refrigerant therein is the discharge gas temperature. In certain applications of the hermetic compressor, as for example, in 'heat pumps, it has been found that the conventional motor protection arrangements are not adequate to assure optimum system operation without unnecessary and undesirable compressor shutdown.

Consider a typical heat pump application. It is known that the compressor refrigerant flow rate is reduced as the outdoor temperature falls. As the outdoor temperature falls, the difference between the temperature of the discharge gas at the discharge valves and the temperature exterior of the compressor becomes greater. For instance at 45 degrees evaporator temperature and 125 degrees condensing temperature, the differential temperature between that at the discharge valves and the outside of the compressor is on the order of 3 to 5 degrees.

However, as the evaporator temperature is reduced from 45 degrees to, for example, degrees, the differential temperature of the discharge gas at the discharge valves and exterior of the compressor increases to 30 degrees or more. Thus, it is evident that if a discharge gas temperature limiting switch is utilized external of the compressor to provide additional compressor protection, the limiting switch will have to be adjusted to compensate for this increased temperature differential in order to protect the compressor.

But, in heat pump applications where the flow rate is very low, if the discharge gas temperature limiting switch is derated in order to accommodate a wide temperature dilferential; then a condition of false sensing results and this could cause shutdown of the compressor unnecessarily when the compressor is in fact operating in a safe zone and there would be no damage to the compressor or to the refrigeration system. Therefore, it is virtually impossible to apply a discharge gas temperature limiting switch external to the compressor which would adequately read the limits of operation of the compressor 'ice under all conditions, including high-load air conditioning applications and very low-load heat pump applications.

In modern high-speed hermetic compressors, the compression mechanism is generally resiliently supported within the sealed outer casing. A part of the discharge conduit is aflixed at one end to the discharge outlet from the compression mechanism and at the other end to the outer casing. The intermediate portion of the discharge conduit forms a shoe loop within the compressor for permitting movement of the compression mechanism with respect to the outer casing without damage to the discharge conduit. Ordinarily, suction gas passes in heat exchange relationship with the shock loop, thereby lowering the temperature of the high pressure vaporous refrigerant being forwarded to the condenser and resulting in a substantial temperature differential between the temperature of discharge gas external to the compressor and the temperature of discharge gas adjacent the cylinders.

An object of the present invention is to provide a hermetic compressor with discharge gas temperature sensing means which are disposed internally of the compressor and within the discharge gas manifold and which are adapted to quickly and accurately control compressor operation under a wide range of operating conditions.

Another object of the present invention is to provide a hermetic refrigerant compressor with discharge gas temperature sensing means which are disposed within the gas muffling chamber in the compressor and which are adapted to function in cooperation with the inherent motor protection means of the compressor to control compressor operation during a wide range of operating conditions. Yet another object of this invention is to provide a hermetic refrigerant compressor having a resiliently supported compressor block with a discharge temperature limiting means which is mounted within the discharge gas mufl ling chamber in such compressor, such discharge gas limiting means comprising a thermostat which is connected to the electric circuit for the compressor motor internally of the compressor. These and other objects of the invention will be more readily perceived from the following description.

The attached drawing illustrates a preferred embodiment of the invention in which:

FIGURE 1 is a perspective view of a hermetic refrigerant compressor, with a portion of the casing being broken away to show the location of the discharge gas temperature limiting means within the compressor;

FIGURE 2 is an enlarged detail view taken generally on the line 2-2 of FIGURE 1 and more clearly illustrating the position of the discharge gas temperature limiting means within the discharge gas mufiling chamber of the compressor;

FIGURE 3 is a side view of the compressor block, with the annular sleeve omitted, illustrating the position of the discharge gas limiting means with respect to two of the cylinders;

FIGURE 4 is a detail cross-sectional view of the discharge gas temperature limiting means talcen generally on the line 44 of FIGURE 2;

FIGURE 5 is a cross-sectional view of the discharge gas temperature limiting means taken generally on the line 5-5 of FIGURE 4; and

FIGURE 6 is a schema-tic wiring diagram of an electric control system for a compressor motor employing the discharge gas temperature limiting means of the present invention.

Referring to FIGURE 1, there is illustrated a refrigerant compressor ?10 which comprises an outer casing enclosing both the compressor motor and the compression mechanism. The outer casing comprises an upper shell 11 and a lower shell 12 suitably joined together to form ahermetic outer casing. The compressor 10 is adapted to be connected to a refrigerant circuit by means of discharge gas fitting 13 and suction gas fitting 14.

The compression mechanism 16 is resiliently supported in the outer casing by means of a plurality of spring means 1 8 which function between a flange on the annular sleeve enclosing the compression mechanism and a coacting flange on a mounting ring 20 mounted on the interior of the outer casing. Reference may be made to the copending application of Sidney A. Parker, Serial N 0. 361,126, filed April 20, 1964, for a more detailed explanation of the compression mechanism and the mounting means therefor.

From FIGURE 1, it is seen that the discharge gas temperature limiting means 22 of the present invention is disposed within the outer casing of compressor 10 and is integrally carried within the compression mechanism 16.

Turning now to FIGURE 2, it is seen that the compression mechanism 16 includes a compressor block or body 24 having an upper peripheral flange 26 and a lower peripheral flange 28 defined thereon. An annular shield or sleeve 30, preferably made from metal, cooperates with the annular flanges 2-6 and 28 on the compressor block 24 to define a discharge gas mufiling chamber 32 about the compression block 24. Within the body 24, are reciprocating pistons which are operatively connected to a drive shaft or crankshaft driven by the compressor motor.

'It is preferred that a heat shield 34 be provided about the annular sleeve 30 to insulate the suction gas entering the compressor 10 through the suction gas fitting 14 from the discharge gas mufiiing chamber 32. This arrangement prevents an undesirable rise in suction gas temperature. A sound-deadening ring 36 may be aflixed internal- 1y to the lower portion 12 of the outer casing in order to reduce the vibrations emanating from the compressor.

The discharge gas temperature limiting means 22 comprises a tubular housing 3 8 preferably made from a heatconduoting material, such as metal, aflixed at its upper end within a bushing 40 which is in turn connected to an opening in the flange 26 on compressor block 24. The tubular housing 38 is closed at its lower end by a capli'ke member 3 9.

Disposed internally of the tubular housing 3 8 is a thermal protection switch or thermostat 44. Extending from the thermostat 44 are leads 46 and 48 for electrically connecting the thermostat 44 into the compressor motor circuit. Preferably, the thermostat 44 is surrounded by a heat transfer material. Such material may comprise a suitable adhesive, such as an epoxy, in order to fix the position of the thermostat 4 4 within the tubular housing 38. It will be understood that the thermostat 44 may be surrounded by a material such as oil if desired, suitably retained with housing 38.

Referring to FIGURE 3, there is shown a side view of a compressor block 24 with the annular sleeve removed so as to better illustrate the position of the discharge gas temperature limiting means '22 between a pair of ad jacent radially disposed cylinders 49 and 50 within the compressor block 24. It will be understood that the compressor block comprises a plurality of cylinders, within which are disposed reciprocating pistons. High pressure vaporous refrigerant is discharged from each cylinder into a peripheral or circumferential pathway 52 defined between the compressor block 24, annular sleeve 30 and flanges 28 and 56 on block or body 24. As is known, the passageway -2 may be provided with restrictions or webs 5 9 for defining mufliing cavities in passageway 52. The discharge gases collected in the passageway '52 pass through an opening 54 in the flange 56 into an upper peripheral passageway 58, which may also be constructed and arranged to define mutfling cavities. From the upper passageway, the discharge gases flow into a discharge conduit (not shown) which communicates with the discharge fitting '13 (FIGURE 1) for passage into the discharge line of the refrigeration system in which the refrigerant compressor 10 is utilized.

Thus, it is evident from FIGURES 1, 2 and 3 that the discharge gas temperature limiting means is disposed in the innards of the compressor in a position to detect the discharge gas temperature at essentially its hottest temperature. There is little variance in the differential of the temperature between that at the discharge valves and the temperature sensed by the discharge gas limiting means 22. Accordingly, a thermostat 44 may be used which has a narrow operating range. As the thermostat 44 is highly sensitive to variance in discharge gas temperature, the refrigerant compressor of this invention may be utilized for heat pump applications having low flow rates or for air conditioning applications having very high flow rates. In each instance, the compressor operation would be optimized. There would be little likelihood of false sensing and premature shut-off of the compressor. Similarly, it will be understood that a dangerous condition would be sensed promptly with accompanying termination of compressor operation.

In FIGURE 4, there is shown an enlarged cross-sectional detail view of the discharge gas temperature limiting means 22. The thermostat 44 is surrounded by a suitable plastic film 60 which is wrapped thereabout in several layers and then imbedded in an adhesive 62, such as an epoxy material, for fixing the position of the thermostat 44 within the tubular housing 38. It will be apparent that the thermostat 44 will be in intimate heat exchange relationship with the hot discharge gases in the discharge gas mufliing chamber 32.

The protector 44 comprises a housing or casing 64 of heat conductive material. Cantilevered within the crimped end 66 of casing 64 is a bimetal 68. The contact 70 on the end of the bimetal 68 engages a contact 72 which is carried on support 74, that is in turn affixed to the lead 48. The lead 46 is affixed to the housing and therefore electrically connected to the bimetal 68 in order to complete a circuit through the protective device 44.

Referring now to FIGURE 6, there is illustrated a schematic wiring diagram utilizing the discharge gas temperature limiting switch of the present invention. The compressor motor 80 is connected to the lines T and T which are in turn connected to a power source. The supply of power to the motor 80 is interrupted when the contacts 81a and 81b of the compressor motor start coil 82 are opened upon actuation of the relay 81.

The contactor relay 81 is disposed in a pilot circuit or low voltage circuit which is connected to a suitable source of low voltage by the lines L and L Provided in circuit with the contactor relay 82 in addition to the discharge gas temperature limiting means 44 are normally closed pressure switches 86 and 88, an external motor overload and an in-winding thermostat 92. The pressure switches 86 and 88 are adapted to sense overload conditions in the refrigerant circuit. The external overload switch 90 is disposed externally of the compressor and is responsive to current overload to terminate operation of the compressor motor 80. The thermostat or protective device 92 is preferably mounted in the stator slots or on the windings of the compressor motor for fast response to motor winding temperature. Upon opening of any one of the normally closed switches in the pilot circuit, the contactor relay 81 will be deenergized, thus opening the contacts 81a and 81b to terminate operation of the compressor motor.

It can be seen that by the present invention, there has been provided a hermetic refrigerant compressor having internal discharge gas temperature limiting means for terminating operation of the compressor under widely divergent operating conditions. The hermetic refrigerant com- The discharge gas temperature limiting means is disposed in the discharge mufliing chamber of the refrigerant compressor so as to detect the temperature of the discharge gas at its source. As there is little temperature differential between the discharge gas temperature at the discharge valves in the ends of the cylinders and in the discharge gas muffiing chamber, a discharge gas temperature limiting means having a very closely calibrated tripping temperature corresponding very closely to a temperature predetermined to provide excellent long life operation can be used, thereby providing a more sensitive control.

While I have shown a preferred embodiment of the present invention, it Will be understood by those skilled in the art that the invention is not so limited, since it may be otherwise embodied Within the scope of the following claims.

I claim:

1. In a reciprocating compressor, the combination of an outer casing, a compressor block resiliently mounted Within said outer casing, compression mechanism within said compressor block, and means defining an annular cavity forming a discharge gas manifold about said compressor block, motor means for driving said compression mechanism, and discharge gas temperature sensing means disposed in said discharge gas manifold, said sensing means including switch means within a heat conductive casing, said switch means being operatively connected to said motor for terminating operation of said motor upon attainment of a predetermined discharge gas temperature.

2. A reciprocating compressor as in claim 1 wherein said casing is retained in position within a housing by a heat transfer adhesive, said housing being affixed to the compressor block and extending into said discharge gas manifold.

3. In a reciprocating compressor of the type having compressor block means resiliently mounted within a hermetically enclosed casing and an electric motor driven compression mechanism in said block means, means on said block means defining an annular discharge gas cavity, the improvement comprising a discharge gas temperature limiting means on said compressor block means and disposed in said discharge gas cavity in intimate heat exchange relationship with the discharge gas for sensing the temperature of said discharge gas at its source, said discharge gas temperature limiting means being operatively associated with the electric motor driving the compression mechanism of the compressor for terminating operation of the compressor motor upon attainment of predetermined discharge gas temperature.

4. A reciprocating compressor as in claim 3 wherein said discharge gas temperature limiting means comprises a housing having switch mean-s enclosed therewithin, said housing being disposed in the discharge gas cavity.

5. A reciprocating compressor as in claim 4 wherein said compressor block means includes an annular flange, said cavity defining means comprising an annular sleeve member on the compressor block means, and said housing is disposed in a second housing affixed to said flange and extends into said discharge gas cavity.

References Cited by the Examiner UNITED STATES PATENTS 2,344,946 3/1944 Landon 23017 2,518,597 8/1950 Brooks 230-17 2,946,203 7/ 1960 Carver 230--117 3,016,183 1/1962 Murphy et al 230-232 3,065,901 11/1962 Neubauer 230-232 MARK NEWMAN, Primary Examiner.

SAMUEL LEVINE, Examiner.

W. L. FREEH, Assistant Examiner. 

1. IN A RECIPROCATING COMPRESSOR, THE COMBINATION OF AN OUTER CASING, A COMPRESSOR BLOCK RESILIENTLY MOUNTED WITHIN SAID OUTER CASING, COMPRESSION MECHANISM WITHIN SAID COMPRESSOR BLOCK, AND MEANS DEFINING AN ANNULAR CAVITY FORMING A DISCHARGE GAS MANIFOLD ABOUT SAID COMPRESSOR BLOCK, MOTOR MEANS FOR DRIVING SAID COMPRESSION MECHANISM, AND DISCHARGE GAS TEMPERATURE SENSING MEANS DISPOSED IN SAID DISCHARGE GAS MANIFOLD, SAID SENSING MEANS INCLUDING SWITCH MEANS WITHIN A HEAT CONDUCTIVE CASING, SAID SWITCH MEANS BEING OPERATIVELY CONNECTED TO SAID MOTOR FOR TERMINATING OPERATION OF SAID MOTOR UPON ATTAINMENT OF A PREDETERMINED DISCHARGE GAS TEMPERATURE. 